This invention relates in general to an automatic apparatus which operates to secure or nail a plurality of pickets transversely on stringers and more particularly to such apparatus for manufacturing picket fences such as stockade and board fences.
The prior art is replete with a number of patents which show and describe machines and apparatus of various types for automatically constructing or nailing slats or pickets transversely on backing rails or stringers. Many of these devices provide a more efficient technique of fabricating such a structure as compared to the hand fabrication of the unit. In any event, there is a need for a more efficient and reliable apparatus which will provide the fence manufacturing industry with a simpler and more efficient method of assembling various heights of picket, stockade and board fences.
In prior art devices certain apparatus employed conveyor belt systems for transporting both pickets and stringers during assembly. These devices were relatively complicated and required much maintenance, as well as operator assistance in order to properly use the device. An example of such a device is depicted in U.S. Pat. No. 4,054,236 issued on Oct. 18, 1977 to G. C. Paxton. This device employs a reversible conveyor which included chucks on the conveyor which operated to grasp and position stringers in parallel relationship. The conveyor operated to advance the structure towards a nailing station in incremental steps where the increments were mechanically controlled by indexing means. Still other patents as U.S. Pat. No. 3,945,549 entitled AUTOMATIC STITCH NAILING APPARATUS issued on Mar. 23, 1976 to D. W. Colson show different techniques. In this patent first and second conveyors are employed and are controlled in sequence. The conveyors are operated to provide alternate movement. The patent shows the use of electromechanical control means which automatically senses the nailing of a slat to the stringers to cause the cycle to repeat.
U.S. Pat. No. 3,576,286 issued on Apr. 27, 1971 to T. J. Bunch entitled AUTOMATIC FASTENING MACHINE, shows a carriage which carries fastening guns and which moves over a work piece to automatically nail slats to stringers.
Other patents as U.S. Pat. No. 3,763,547 and U.S. Pat. No. 4,039,112 depict different apparatus for fastening slats to stringers.
As one can ascertain, the prior art is replete with many patents which relate to different mechanisms for performing the same function, that is, such prior art patents are concerned with the attachment of slats or pickets to stringers or backing rails automatically and as rapidly as possible. As one can ascertain by reading the above noted patents, such devices are extremely complicated and consist of many moving parts and are therefore both difficult to use and to maintain.
It is therefore an object of the present invention to provide an automatic apparatus for attaching pickets to stringers which machine is relatively simple, in that it employs few moving parts while providing rapid operation.
The machine to be described employs pneumatic cylinders and valves which control a reciprocating carriage assembly. A predetermined number of pickets are stacked vertically in a hopper which hopper is mounted in proximity to the carriage assembly. As the carriage reciprocates, the lower most picket is pushed on to a stringer assembly, and based on the machine operation, is secured in place by means of pneumatic nailing assemblies which are synchronized to activate by means of a rotatable offset shaft assembly which moves the nailing assemblies in a closed arcuate path as synchronized by the movement of the carriage.